In the dispensing of liquids and semi-liquids such as viscous liquids or thick liquids, including catsup, mustard, salad dressing, or other food products or medicinal products, there has been the difficulty of effectively and in a sanitary manner forcibly dispensing all of the liquids from the container outlet. With containers of this type and in the attempted dispensing thereof, some of the liquids remain within the container and are wasted.
Previously, a flexible balloon has been used within a container for propelling the contents from the outlet thereof. However, difficulties have been encountered in controlling the flow of pressurized air into and out of the balloon such that upon release of pressure from the pump mechanism, the dispensed liquids return to the container. In addition, the prior art devices using air pumps have resulted in some air contamination of the liquids being dispensed.